1. Field of the Invention
The present invention relates to an electronic device, such as a multilayer ceramic capacitor, and the production method, and particularly relates to an electronic device having low IR temperature dependency and a reliable average lifetime, etc. and the production method.
2. Description of the Related Art
A multilayer ceramic capacitor as an electronic device is widely used as a highly reliable compact electronic device having a large capacity, and the number to be used in an electric apparatus is also large. In recent years, as apparatuses becoming more compact with higher performance, demands for a multilayer ceramic capacitor to be more compact, larger in capacity, lower in price, and higher in reliability have increasingly become stronger.
The multilayer ceramic capacitor normally produced by stacking an internal electrode layer paste and a dielectric layer paste by a sheet method or a printing method, etc. and co-firing internal electrode layers and dielectric layers.
As a conductive material of the internal electrode layers, Pd and a Pd alloy are generally used, but due to a high price of Pd, relatively inexpensive base metals, such as Ni and a Ni alloy, have come to be used. When using a base metal as a conductive material of the internal electrode layers, co-firing of the dielectric layers and the internal electrode layers has to be performed in a reducing atmosphere because firing in the air results in oxidization of the internal electrode layers. However, when firing in a reducing atmosphere, the dielectric layers are reduced and the specific resistance is liable to decline. Therefore, a non-reducing dielectric material has been developed.
However, in multi-layer ceramic capacitors using a dielectric ceramic composition, IR (insulation resistance) remarkably deteriorates due to an electric field application, namely, there is a disadvantage that an IR lifetime is short and the reliability is low.
Also, a preferable temperature characteristic of a capacity is also demanded in a capacitor and, particularly, the temperature characteristic of the capacity is demanded to be flat under a strict condition depending on the use object. In recent years, multilayer ceramic capacitors have come to be used in a variety of electronic devices mounted in engine compartments of automobiles, such as an electronic control unit (ECU), a crank angle sensor and an Anti Lock Brake System (ABS) module. Since these electronic devices are for stable engine controlling, drive controlling and brake controlling, preferable temperature stability of the circuit is required.
To overcome the disadvantages, for example, the Japanese Patent Publication No. 3348081 discloses a dielectric ceramic composition, wherein a containing ratio of rare earth oxides is made high comparing with a conventional X7R-characteristic material and a content of an oxide of an element selected from Mg, Ca, Ba, Sr and Cr is 0.1 to 3 moles. According to the invention described in the article, since easily evaporating Pb, Bi and Zn are not included, firing in a reducing atmosphere becomes possible, so that it is possible to obtain a dielectric ceramic composition, wherein a temperature characteristic of the capacity can be improved and the X8R characteristics are satisfied.
Also, the Japanese Patent Publication No. 3341003 discloses a dielectric ceramic composition satisfying the X8R characteristics even if it is made thin by decreasing a content of an oxide of an element selected from Mg, Ca, Ba and Sr comparing with the dielectric ceramic composition of the Japanese Patent Publication No. 3348081. According to the invention described in the article, the X8R characteristics can be obtained without using an expensive lanthanoid among rare earth oxides.
However, although the temperature dependency of the capacity is improved in the inventions described in the above articles, there is a disadvantage that the IR temperature dependency is large and deterioration of resistance (IR) is particularly notable when used under a high temperature and the reliability becomes poor.